lib/future.cpp

The following code example is taken from the book
C++ Move Semantics - The Complete Guide by Nicolai M. Josuttis, Leanpub, 2020
The code is licensed under a Creative Commons Attribution 4.0 International License.

---

// raw code

#include <iostream>
#include <string>
#include <vector>
#include <thread>
#include <future>

void getValue(std::promise<std::string> p)
{
  try {
    std::string ret{"vote"};
    //...
    // store result:
    p.set_value_at_thread_exit(std::move(ret));
  }
  catch(...) {
    // store exception:
    p.set_exception_at_thread_exit(std::current_exception());
  }
}

int main()
{
  std::vector<std::future<std::string>> results;

  // create promise and future to deal with outcome of the thread started:
  std::promise<std::string> p;
  std::future<std::string> f{p.get_future()};
  results.push_back(std::move(f));

  // start thread and move the promise to it:
  std::thread t{getValue, move(p)};
  t.detach();  // would not be necessary for std::jthread
  //...

  // wait for all threads to end:
  for (auto& fut : results) {
    std::cout << fut.get() << '\n';
  }
}